Active sound control systems often require, in addition to actuator and electronic control components, specialized sensor devices. The requirements associated with such sensors to a large part are determined by the particular active control approach employed, as well as the kind of performance expected of the sound controlling system. One type of sensor is the microphone, which measures sound or the existence of atmospheric pressure waves in a particular area of interest.
These sensors are often used as components of instrumentation packages employed on missiles, satellites or other rocket payloads, aircraft or other mechanisms in which atmospheric pressure waves, acceleration or vibration can be quite severe. When in employed in such environments, weight becomes a critical variable. A 10 gram weight differential at rest becomes a 150 gram weight difference during a 15 G acceleration event.
While various electro magnetic microphones offer high levels of sensitivity and good performance in terms of size and efficiency, these electromagnetic devices are often very sensitive to EMI and aren't always physically robust. The hardening of these devices to EMI almost invariably causes an increase in physical size, weight, sensitivity and expense.
The main emphasis has been given to phase modulated interferometric fiber optic sensors for detecting pressure and strain. Though interferometric type sensors offer very high sensitivity, polarization effects and high cost have delayed the implementation of these sensors to commercial applications. Frequency modulated sensors utilizing fiber gratings are very promising for monitoring strain in different location along one fiber.
One solution is to employ microphones that are not electrical or semiconductor in nature. The use of fiber optics for sensors in general, and for sound detection in particular, are one option available to designers which simultaneously solves the EMI sensitivity, size and weight problems inherent in electrical sensors.
Since fiber optics use light rather than electricity, a fiber optic microphone is generally insensitive to EMI, or EMF and is therefore more efficient in an environment that has a large amount of electro magnetic energy. As a result, fiber optic microphones can be located adjacent to or actually attached to electronic devices that generate large electro magnetic fields without negative affects to either the microphone or the area of interest.
Intensity modulated fiber optic sensors, while often less sensitive than comparable interferometric sensors, are simpler and less expensive.
Therefore it is an object of this invention to offer an intensity modulated fiber optic pressure sensor that is small and lightweight.
It is yet a further object to offer a pressure sensor that is EMI insensitive.
It is a further object of this invention to offer a pressure sensor that features high levels of sensitivity.
It is a yet another object offer a pressure sensor that is physically robust.
It is a further object of this invention to offer a pressure sensor that is economical.